1. Field of the Invention
The present invention relates to a reflection preventing film which is useful for microprocessing in lithographic processes using various radiations, and to a process for forming a resist pattern using the reflection preventing film.
2. Description of the Background Art
In the filed of production of integrated circuits, a lithographic process which enables fine processing in an order of sub-half micron is now being developed in order to obtain a higher degree of integration.
In this lithographic process, a desired pattern is obtained by coating a resist such as a positive resist consisting of a novolak resin and a quinonediazide sensitizer usually in a thickness of 0.5-10 .mu.m on a substrate, transferring the master pattern thereto using a stepper, and then developing the same with a suitable developing solution.
However, due to halation caused by reflection of the incident radiation on the surfaces of highly reflective substrates, such as aluminum or aluminum alloys (e.g., aluminum-silicon alloy, aluminum-silicon-copper alloy), polysilicon, and tungsten silicide, used in this process, or even on the surfaces of other materials such as silicon which are used depending on the wavelength of radiation (e.g., deep ultraviolet rays), the radiation reaches the region which should not be irradiated. This prevents precise reproduction of fine patterns. A conventional method for preventing reflection on the surfaces of substrates has been adding a radiation absorber, such as a dye, to the positive resist to reduce transmittance of radiations of the resist.
The method of adding a radiation absorber, however, does not allow radiations to reach sufficiently deep in the resist coating film. This can be the cause of problems such as impaired resist pattern configurations, decrease in the sensitivity, resolution degree, depth of focus or the like, and reduced resist storage stability. The resist performance is lowered, resulting in impaired development and resolution performance.
Another method proposed for preventing the halation is forming a reflection preventing film on the surfaces of highly reflective substrate to absorb the incident radiation. Inorganic films such as coating layers of titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, and .alpha.-silicon, formed by vacuum deposition, CVD, spattering, or the like, are known as such a reflection preventing film. These inorganic reflection preventing films have problems in their applicability to integrated circuits because of their conductivity and in the requirement of special devices for vacuum deposition, CVD, or spattering, when they are formed.
In an attempt for overcoming these problems in the inorganic reflection preventing films, an organic reflection preventing film comprising a polyamine acid (co)polymer or sulfone (co)polymer and a dye has been proposed (for example, Japanese Patent Application Laid-open (kokai) No. 93448/1984). This reflection preventing film is not conductive and can be applied to substrates by the same method as the method of resist application by dissolving it in a suitable solvent without requiring a special device.
However, this reflection preventing film comprising a polyamine acid (co)polymer or sulfone (co)polymer and a dye has the following problems. (i) Halation cannot be prevented sufficiently because of a limitation to the amount of dyes to be added. (ii) Halation preventing effects are unduly decreased and the equipment is contaminated due to sublimation of a portion of dyes from the reflection preventing film during baking and dry etching operation. (iii) Resist resolution and development performance are impaired due to intermixing (a phenomenon that a slight amount of the components of the reflection preventing film is mixed with the resist). (iv) Deformation of resist patterns during the baking and dry etching operation after irradiation due to poor heat resistance of the reflection preventing film. (v) Resist patterns may be damaged or cannot be precisely transferred to the reflection preventing film by the dry etching method after development, because the etching speed of the reflection preventing film is equivalent to or less than that of the resist.
An object of the present invention is therefore to provide a reflection preventing film, exhibiting a high halation preventing effect, involving no sublimation of radiation absorbing components contained therein, free from occurrence of intermixing, possessing excellent heat resistance, exhibiting a superb dry etching performance and storage stability, and producing resist patterns with excellent resolution capability and precision, as well as a process for forming resist patterns.